The present invention relates to a method of forming a plastic plate. More particularly, the present invention relates to a method of forming a shaped product having a high rigidity in which an inorganic filler is oriented in the entire layer of a plate-like body, or an extruded product having layers of different hue and composition wherein a thermoplastic resin containing a flake-like inorganic filler (hereinbelow, referred to as a filler-containing resin) or a thermoplastic resin without containing filler (hereinbelow, referred to as a sole resin) discharged in a molten state from an extruder is formed into a plurality of plate-like bodies under a back pressure in a single former, and then, the platelike bodies are merged into a single body in the former.
DESCRIPTION OF THE RELATED ART
There has been known a method of forming a plate-like body wherein a resin, particularly a resin having crystallizability such as polypropylene, polyamide or the like is melt-extruded into a former while a back pressure is applied to the molten resin to thereby form the resin into a predetermined shape in a former. The plate-like body obtained by this method is a single-layered molded product.
In order to impart rigidity to the plate-like molded product, a method wherein a flaky or fibrous inorganic filler is added to a resin and thus obtained mixture is molded has been generally used.
However, there is a limit to the increasing of the rigidity on the molded product when a large amount of the filler is added to the resin to obtain a high rigidity, and there may occur molding fault.
Further, when it is necessary to form a thick-walled molded product wherein the hue or composition is different between an outer layer portion and the opposite layer portion, or an intermediate layer and the outer layer portions, a method wherein a plurality of single-layered molded products each having different hue and composition are formed by extrusion-molding, and the single-layered molded products are laminated and melt-bonded by a heat roll method or a heat press method, is generally used.
However, the above-mentioned method requires many steps of shaping and is complicated, which reduces processability and requires a great energy consumption. Further, there easily occur color change and denaturation because the heat history of the resin is large and the quality of a molded product is adversely effected.